In ITS (Intelligent Transport Systems), inter-vehicle communication for exchanging information between vehicles using radio waves has been investigated, and multi-hopping, i.e., data transfer by way of multiple communication apparatuses has also been contemplated as practical specifications.
In particular, in ETSI ITS (European Telecommunications Standards Institute ITS), a plan has been developed in which, when an onboard unit (communication apparatus) engaged in the communication carries out multi-hop communication, two communication channels are used as its communication channels, and the communication channels are switched between the first stage (control channel: CCH), the second and the following stages (service channel: SCH) (see Patent Document 1, for example).
In order to realize this operation, all the onboard units have to be ones that can use two channels.